Lighting device and electrical connection therefor



June 15, 1965 w. J. KNOCHEL 3,189,786

LIGHTING DEVICE AND ELECTRICAL CONNECTION THEREFOR Filed Aug. 10. 1960 Ii a 5 v a 4 2 1 United States Patent 3,189,786 LKGHTING DEVICE ANDELECTRICAL CUNNEIITEQN THEREFOR William Ii. Knochel, West Grange, Nl,assigncr to Westinghouse Electric Corporation, East Pittsburgh, Pa, a

corporation of Fennsylvania Filed Aug. 10, 1966, Ser. No. 43,661 Claims.(Cl. 315-71) This invention relates to electric lighting devices and,more particularly, to an electroluminescent lamp and an improvedelectrical connection therefor.

In order to protect the phosphor employed in electroluminescent devicesfrom the deteriorating effects of Water vapor and contaminatingatmospheric gases it is necessary to seal these portions of the devicesthrough which such gases could penetrate. In glass-plastic type lampsthis is accomplished by coating the back and sides of the lamp with asuitable thermosetting plastic such as epoxy or the like, or byencapsulating the entire lamp in such material. In ceramic type lampsthe desired vapor barrier is provided by firing a protective glass layerover the glass-phosphor layer or front of the lamp.

While such protective layers prevent the ingress of contaminating gasesthey present a problem in that the power leads or lead-in conductorsmust frequently be hermetically sealed therethrough. This is difiicultto accomplish, particularly when the lamps are exposed to a wide ambienttemperature range insofar as the conductor tends to tear away from theseal because of the diiferen tial in the coeflicient of expansion of theconductor and the vitreous or plastic layer. In addition, due to the lowcurrent rating of such electroluminescent devices the leadin conductorsmust be maintained in positive contact with the lamp at all times tokeep the contact resistance as low as possible. Thus, a hermetic sealaround the leadin conductors and a low-resistance juncture between suchconductors and the lamp contacts are essential if the lamp is to havegood life performance, particularly under varying ambient temperatureand high humidity conditions.

This problem of effecting a durable low-resistance connection betweenthe device contacts and the lead-in conductors is even more complicatedwhen a prong type leadin conductor is employed and an arc-suppressingseries resistor is interposed between the end of the conductor and thelamp contacts insofar as only l-ine contact is effected between theresistor and lead-in conductor. A combination arc-suppressing andelectrical connection of this type is disclosed and claimed in copendingU.S. application, Serial No. 42,931, of G. Saviers, filed July 14, 1960,now Patent No. 3,121,817, assigned to the assignee of the presentinvention.

With the foregoing in mind it is the general object of this invention toprovide an improved electroluminescent lighting device which will have along useful life even when operated under high humidity and varyingambient temperature conditions.

Another and more specific object is the provision of an electrical powerconnection for an electroluminescent lamp or similar device which can bevery conveniently and inexpensively fabricated and will not deteriorateunder adverse operating conditions.

Still another object is the provision of an electrical ice powerconnection that is hermetically sealed and will withstand a wide rangeof ambient temperature.

The aforesaid objects, and others which will become apparent as thedescription proceeds, are achieved by using a layer of highly conductivematerial such as silver or the like to connect the lead-in conductorsand lamp contacts, which layer is firmly bonded to and sealed within theprotective layer of glass or plastic applied to the lamp and over thecontacts. The conductive material is placed in contact with theprotective material while it is still in a fluid state and thus forms aplating thereon when the material hardens which plating effects asealed-in lowresistance juncture between the lead-in conductor and lampcontacts that is very durable and inexpensive to fabricate.

A thin strip of highly conductive material may also be used as thelead-in conductor itself to provide a ribbon or foil type conductor thatis hermetically sealed through the protective non-conductive layer andextends to any desired point on the exposed surface thereof.

A better understanding of the invention will be obtained by referring tothe accompanying drawing wherein:

FIG. 1 is a perspective view of a plugin electroluminescent lightingunit which incorporates the present invention;

FIG. 2 is an enlarged cross-sectional view along the line II-II of FIG.1, in the direction of the arrows;

FIG. 3 is a perspective view of the electroluminescent lamp componentemployed in the lighting unit shown in the preceding figures, thecentral portion of the lamp being removed for convenience ofillustration;

FIG. 4 is an enlarged side elevational view of one end of the lightingunit shown in FIGS. 1 and 2;

FIG. 5 is a perspective view of one of the resilient leadin prongconductors;

FIG. 6 is a perspective view of one of the resistor elements; and

FIG. 7 is a view corresponding to FIG. 4 but shows another form ofelectrical connection according to the present invention.

With specific reference to the drawing, in FIGS. 1 and 2 there is showna lighting unit 10 comprising an electroluminescent lamp 12 that ismounted in a frame 1 10f plastic or the like. As shown more particularlyin FIG. 2, a pair of prongs 17 and 19 project from the back of thelighting unit to provide plug-in terminals which prongs constitute theouter ends of generally L-shaped resilient lead-in conductors 26 and 27that are rigidly anchored to and project through a back panel 16'secured to the back of the frame 14. The inner ends of the aforesaidlead-in conductors are compressed against flat composite type limitingresistors 30 and 32 which, in turn, overlie and connect with bus-bars orcontacts 28 and 29, respectively, on the back of the lamp. A layer ofcured plastic 25 (FIGS. 2 and 4) such as epoxy or the like is cast overthe back of the lamp 12 and around its edges to provide the necessaryvapor barrier and permanently seal the lamp within the frame. The innerends of the lead-in conductors 26 and 27 are embedded in and rigidlyheld in operative relation with the lamp and the aforesaid resistors bythe protective layer 25.

As shown in FIGS. 2 and 3, the electroluminescent lamp 12 is of theglass-plastic type and comprises, in the following order, a glass baseplate 18, an overlying light-transmitting electrode 20 such as tin oxideor the like, an electroluminescent phosphor-dielectric layer 22 and asecond electrode 24 of vaporized aluminum or the like. A pair ofbus-bars or contacts 28 and 29 are provided along opposite side edges ofthe back of the lamp by applying strips of silver paint or the like. Thecontact 28 is connected to the light-transmitting electrode 20 whereasthe contact 29 connects with the metallic elec trode 24 through anoverlapping extension thereof, as shown. The exposed surface of thecontact 29 accordingly comprises the overlying part of the metallicelectrode 42. The limiting resistors 30 and 32 are of the composite typeand of generally rectangular configuration the flat surfaces whereof areprovided with a coating 34 of suitable highly conductive material suchas copper or the like, as shown in FIGS. 2 to 4 and FIG. 6. A moredetailed description of the lighting unit and limiting resistorsand modeof assembly thereof is given in the previously referred to copendingapplication of George Saviers and in copending US. application SerialNo. 825,961, of W. J. Knochel et al., filed July 9, 1959, whichapplication now Patient No. 3,056,898, which. is also assigned to theassignee of the present invention.

In accordance with the present invention the desired positive juncturebetween the lead-in conductors 26 and 27 and the resistors 30 and 32 isachieved by providing a coating 36 of highly conductive material such assilver or the like on the end of the conductors. Only the end segment ofthe. lead-in conductors that is subsequently embedded in the protectivelayer 25 is coated, as shown in FIG. 5. Thus, when the lamp 12 is placedinto the frame 14 and the back panel 16 is snapped in place, after theplastic 25 is cast over the back and sides of the lamp, the coated endsof the lead-in conductors are pressed into and through the plasticmaterial and against the copper-coated surfaces of the limitingresistors 30 and 32, as shown in FIGS. 2 and 4. It has been found thatduring curing of the plastic layer 25 the silver'coating 36 becomesfirmly bonded to the contiguous surfaces thereof forming a continuousplating thereon that electrically connects the leadin conductors andcopper-coated surfaces of the resistors. In this manner a positivelow-resistance juncture is provided which is embedded within and thushermetically sealed from the atmosphere by the protective plastic layer25.

Experience has shown that the plating formed on the surrounding surfacesof the protective layer 25 by the adhesion thereto of the coating 36 issuch that it forms a highly conductive ribbon-like conductor which isvery durable and is bonded to the copper-coated resistors. This wasdiscovered when lighting units fabricated in accordance with theforegoing were taken apart and the prong lead-in conductors 26 and 27very carefully removed from the protective layer 25. The lamps were thenplaced in a humidity cabinet for over six weeks and upon being removedoperated at their rated voltage simply by making contact with the silvercoating 36 that had becomebonded with and adhered to the plastic layer.This shows that the plating forms a continuous low-resistance path thatextends along the embedded end of the prong conductor and, in effect,serves as a second lead-in conductor which is extremely durable and notaffected by temperature variations orhigh humidity conditions.

It should be noted that even-if the prong conductors 26 and 27 shouldtear away from the protective layer and become separated from theirrespective resistors because of extreme temperature variations to whichthe lamp is subjected in use or shipment, apositive connection willstill be maintained insofar as the ends of the prongs will elfectsliding contact wth the aforesaid plating.

While the protective layer 25 as here shown comprises a layer ofplastic, the same type of sealed in low-resistance connection obviouslywould be obtained if the protective layer comprised a layer of glass, aswould be the case in ceramic type electroluminescent lamps. In addition,it will also be obvious that the limiting resistors 30 and 32 could beomitted if desired and connection made directly with the lamp contacts28and 29.

In FIG. 7 there is shown an alternative embodiment of the presentinvention wherein a thin layer of highly conductive material such assilver paint or the like is sealed through the protective layer 25 ofinsulating material to provide a ribbon lead-in conductor'38 thatconnects the lamp contact (or resistor 34' as here shown) to a point onthe exposed surface of the aforesaid layer. This type connection can bevery readily fabricated by embedding a suitable member in the protectivelayer 25 during the assembly of the lamp 12 and the frame 14 and, afterthe plastic or glass has hardened, removing the aforesaid member toprovide a cavity that extends through the protective layer to theconductive coating 34 on the resistor 32. The walls of the cavity arethen painted with silver paste or the like to provide a thin continuousconductive strip 38 that may be extended to any point on the exposedsurface of the protective layer and the back of the lamp. The cavity isthen filled with epoxy or other hardenable insulating material toprovide a plug that hermetically seals the cavity and the inner segmentof the conductive strip38 therein.

In this manner, a ribbon type lead-in conductor is provided whichenables the lamp contacts, in effect, to be extended to any point on theback of the lamp without exposing the phosphor layer to the atmosphere.This type connection would be especially advantageous in the manufactureof digital electroluminescent devices, for example, where connections toa plurality of discrete segments are required. To prevent leaky sealsthe conductive strip 38 should be kept as thin as possible consistentwith the required current-carrying capacity. Satisfactory results havebeen obtained by maintaining the thickness between about 0.0002" and0.01".

As in the case of the first embodiment shown in FIGS. 2 to 4, the ribbontype lead-in conductor construction shown in FIG. 7 can also be employedin ceramic type electroluminescent lamps in which case the protectivelayer 25 would comprise a vitreous rather than a plastic layer.

It will be apparent from the foregoing that the objects of the inventionhave been achieved by providing a very inexpensive and reliable electricpower connection for an electroluminescent device which is not aifectedby the deteriorating eifects of high humidity conditions and extremetemperature variations.

While several embodiments have been illustrated and described in detail,it will be understood that various modifications in the configurationand arrangement of parts can be made without departing from the spiritand scope of this invention.

I claim:

1. In a lighting device, the combination comprising: an electricalcontact on an exposed part of said device, a body of insulating materialcompletely covering said contact and sealing it off from the atmosphere,and a thin layer of electrically conductive material connected to saidcontact and hermetically bonded to and'sealed through said insulatingbody and extending therealong to a point on the exposed surface thereof.

2. In an electroluminescent lighting device having a pair of electrodes,the combination comprising a contact integral with said lighting deviceand connected to one of said electrodes, a layer of electricallynon-conductive material protectively covering said contact and asubstantial adjoining portion of said light source, a lead-in conductorhaving one end embedded in said non-conductive protective layer andanchored thereby in close proximity to said contact, and a layer ofelectrically conductive material between and connecting the embedded endof said lead-in conductor and said contact, said layer of conductivematerial being firmly bonded to the contiguous surface of saidnon-conductive layer and thereby providing a sealed-in low-resistancejuncture between said lead-in conductor and said contact.

3. The combination as set forth in claim 2 wherein said layer ofelectrically conductive material extends beyond the end of said lead-inconductor and forms a continuous plating on the surrounding surface ofsaid protective layer.

4. The combination as set forth in claim 2 wherein said contactcomprises one face of a composite type resistor connected in seriesbetween one of the device electrodes and said lead-in conductor.

5. The combination as set forth in claim 2 wherein, said contact islocated on the back of said lighting device, said lead-in conductorcomprises a resilient member that is pressured against said lightingdevice, and said protective layer covers the back of said lightingdevice.

References Cited by the Examiner UNITED STATES PATENTS 625,395 5/99Houston 3l768 2,168,769 8/39 Fisher 317-66 2,650,310 8/53 White.

2,774,004 12/56 Jafiee. 2,901,652 8/59 Fridrich. 2,922,912 1/ 60 Miller.2,983,837 5/61 Mash.

FOREIGN PATENTS 764,867 1/57 Great Britain.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner.

2. IN AN ELECTROLUMINESCENT LIGHTING DEVICE HAVING A PAIR OF ELECTRODES,THE COMBINATION COMPRISING A CONTACT INTEGRAL WITH SAID LIGHTING DEVICEAND CONNECTED TO ONE OF SAID ELECTRODES, A LAYER OF ELECTRICALLYNON-CONDUCTIVE MATERIAL PROTECTIVELY COVERING SAID CONTACT AND ASUBSTANTIAL ADJOINING PORTION OF SAID LIGHT SOURCE, A LEAD-IN CONDUCTORHAVING ONE END EMBEDDED IN SAID NON-CONDUCTIVE PROTECTIVE LAYER ANDANCHORED THEREBY IN CLOSE PROXIMITY TO SAID CONTACT, AND A LAYER OFELECTRICALLY CONDUCTIVE MATERIAL BETWEEN AND CONNECTING THE EMBEDDED ENDOF SAID LEAD-IN CONDUCTOR AND SAID CONTACT, SAID LAYER OF CONDUCTIVEMATERIAL BEING FIRMLY BONDED TO THE CONTIGUOUS SURFACE OF SAIDNON-CONDUCTIVE LAYER AND THEREBY PROVIDING A SEALED-IN LOW-RESISTANCEJUNCTURE BETWEEN SAID LEADIN CONDUCTOR AND SAID CONTACT.